If my wife saw this headline, she’d probably fall over laughing. OK, so maybe I don’t fit the classic profile of a happy person. And maybe I shouldn’t be dispensing advice on how to be happy. But I do know what makes people miserable. And it’s no coincidence that the same thing destroys careers and entire companies.

Now, before I tell you what creates more personal and professional misery than anything else and what, conversely, you should always avoid if you want to lead a happy life, let me ask you a personal question: Have you ever lied to yourself?

Don’t answer right away. Take your time and really think about it. Seriously. It’s not exactly the kind of question you get asked a lot … or are likely to be asked again. But it may be the most important question you’ve ever asked yourself so, if I were you, I’d give it some serious thought.

And while I don’t know you from Adam, I can tell you one thing with great certainty: Your answer should be “yes.” And yet, maybe half of you will say “no.” The funny thing is, those who said they do lie to themselves are actually more honest with themselves than those who think they don’t.

That’s because we all lie to ourselves so often in so many ways it isn’t funny:

When you chronically eat foods that are bad for you and don’t get enough exercise, you tell yourself it’s OK but you know it isn’t.

When you exaggerate your accomplishments or claim to be what you’re not on your “About” page, your bio, or your social-media profiles, you tell yourself everyone does it and you have to “fake it ‘til you make it” when, in reality, neither is true.

When you tell yourself that it’s someone else’s fault that you’re not doing better in your career or that bad things keep happening to you, deep down you know that isn’t true; you’re just not willing to face the truth.

When you treat others like crap – acting out in self-righteous anger, in jealous rage, or by making empty threats – you tell yourself they deserve it when, in reality, you lack the courage to face your true feelings of fear, shame, and inadequacy.

When you’re deceitful at work or in your business – committing fraud, providing bad advice for selfish reasons, taking money you didn’t earn, or making commitments you can never meet – you must have some sort of twisted logic to justify it.

I can go on but I’m sure you get the point. And you’ve got to admit, there’s some pretty heavy stuff in that list. Stuff most of us have done at one time or another. And trust me when I tell you, it will come back to haunt you. What goes around really does come around. And it will make you miserable.

I should know. I’ve done some of those things myself. The good news is I’ve been around for ages and started facing my demons long ago. That’s when the truth began to dawn on me that not being honest with yourself is a silent killer. It’s the single most preventable source of personal and professional destruction.

If you want to lead a reasonably happy life and have a fulfilling career, the secret is simply to be honest with yourself. Simple, but far easier said than done.

I’m sure you’ve heard Henry David Thoreau’s famous quote from Walden: “The mass of men lead lives of quiet desperation.” The reason it’s so well known is that it resonates with so many people in so many ways. But to me, it’s always meant that it’s all too easy to trap ourselves in cages of our own design.

If you consider that Thoreau made that great philosophical leap while living in simplicity and solitude in a cabin near Walden Pond for just over two years, it reveals one of life’s great ironies: We lie to ourselves because we want material things we don’t need or deserve. That’s what makes us miserable.

Steve Tobak

Steve Tobak is a management consultant, columnist, former senior executive, and author of Real Leaders Don’t Follow: Being Extraordinary in the Age of the Entrepreneur (Entrepreneur Press, October 2015). Tobak runs...